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Pliant does MLC flash

Cheaper flash storage array drives

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The march of MLC flash into mainstream enterprise storage took another step forward today as Pliant launched its Enterprise Flash Disk (EFD) products.

Pliant is a startup focused on competing with industry leader STEC to supply solid state drives (SSD) as hard disk drive replacements for storage arrays, where they provide a top tier of storage offering the fastest data I/O. Pliant first offered single-level cell (SLC) flash, the fastest and most expensive, and has now moved on to providing a 2-bit multi-level cell (MLC) range that is slower, but still faster than hard drives, while being less expensive than SLC product.

MLC drives in general have limited write endurance compared to SLC flash. Pliant's MLC drives features a proprietary ASIC (application-specific integrated circuit) providing extended write endurance and data reliability features. There are two products, the Lightning LB 200M and 400M, with 200GB and 400GB capacities. They come in the 2.5-inch format, and have a 3Gbit/s SAS interface, with four fully independent full duplex ports. 6Gbit/s SAS is now expected next year, it having been originally intended to arrive some time this year.

Pliant has not provided peak I/O rates, saying these are often based on write data caching in the SSD and don't reflect sustained, real-world performance. It says the LB 400M offers more than 10,000 IOPS with a 70/30 read/write mix of 4KB data blocks. The LB 200M offers more than 8,000 such IOPS. Both these figures exclude write data caching, as the products don't have a write cache.

The total sustained IOPS rate for the 400M is above 25,000 with the 200M having more than 20,000. For comparison Pliant's LB 150S SLC product offers more than 120,000 - quite a performance gap. The sustained read and write data transfer rates are 270MB/sec and 100MB/sec for the 400M, and 240MB/sec and 100MB/se for the 200M. The SLC product offers 420MB/sec and 220MB/sec respectively.

There are unlimited writes during the five year lifetime of these MLC drive. Data security measures including background Patrol Read and Memory Reclaim to speed the write process, extended ECC, triple-redundant ECC protected metadata, and support for the T10 Data Integrity Field (DIF) standard.

We have SLC SSDS available as a tier zero in storage arrays. Since 15,000rpm Fibre Channel or SAS drives represent a tier one it seems we'll have to call the MLC flash drives tier 0.5 storage. What might happen is that SLC flash goes into high-end storage arrays, the V-MAX and DS8000 type products, with MLC drives going into the mid-range modular arrays, the CLARiiONs, EVAs and DS4000s. It's unlikely arrays will use both SLC and MLC flash as the performance difference is not that great considering the amounts of highly active data involved.

EMC has announced the availability of less expensive MLC flash drives, and these are thought to be based on Micron product.

Pliant's Lightning LB 200M and LB 400M are being delivered for OEM evaluation and qualification, and will be available via authorised Pliant channel partners in October. ®